Oxidative dehydrogenation of alkenes or alkadienes to furan compounds

ABSTRACT

Alkenes and/or alkadienes are contacted with molecular oxygen and an oxidative dehydrogenation catalyst consisting essentially of phosphorus, vanadium, oxygen, and at least one promoter selected from the group consisting of iron, cobalt, nickel, and molybdenum to produce furan compounds.

United States Patent Farha, Jr. et al.

Oct. 14, 1975 OXIDATIVE DEHYDROGENATION OF ALKENES OR ALKADIENES TOFURAN COMPOUNDS Inventors: Floyd E. Farha, Jr.; Marvin M.

Johnson; Donald C. Tabler, all of Bartlesville, Okla.

Phillips Petroleum Company, Bartlesville, Okla.

Filed: July 19, 1973 Appl. No.: 380,724

Assignee:

US. Cl. 260/3461 R; 260/680 E; 252/435 Int. Cl. C07D 307/36 Field ofSearch 260/3461 R References Cited UNITED STATES PATENTS 2/1973 Ripley260/3461 R OTHER PUBLICATIONS Ai, Kogyo Kagaku Zasshi, 1971, 74(2), p.183-186, Chemical Abstracts, 1971, Vol. 74, 125302.

Primary ExaminerNorma S. Milestone Assistant ExaminerBernard DentzABSI'RACT 16 Claims, No Drawings OXIDATIVE DEHYDROGENATION OF ALKENES ORALKADIENES TO FURAN COMPOUNDS This invention relates to oxidativedehydrogenation catalysts and the use thereof for the conversion ofalkenes and/or alkadienes to furan compounds.

Furan compounds can react readily with oxygen under oxidation conditionsto produce ring cleavage and the formation of polymers. Accordingly, theproduction of furan compounds by the oxidative dehydrogenation ofhydrocarbons has generally been avoided. Recently it has been discoveredthat furan compounds can be produced by the oxidative dehydrogenation ofhydrocarbons in the presence of certain specific catalysts withoutsubstantial conversion of the furan compounds to undesirable products.The search for additional catalysts suitable for this reactioncontinues.

Accordingly, it is an object of the present invention to provide a newand improved oxidative dehydrogenation catalyst. Another object of theinvention is to pro vide a new and improved process for the conversionof alkenes or alkadienes to furan compounds. Other objects, aspects, andadvantages of the invention will be apparent from a study of thespecification and the appended claims. k

In accordance with the present invention there is provided aniimprovedcatalyst for the production of furan type compounds from unsaturatedacyclic hydrocarbons having from 4 to 10 carbon atoms, which catalystconsists essentially of vanadium, phosphorus, oxygen and at least onepromoter selected from the group consisting of iron, cobalt, nickel andmolybdenum.

If desired, these catalysts can be supported on conventional solidcatalytic support materials, for example, zinc oxide, silica, alumina,boria, magnesia, titania, zirconia, and mixtures thereof. Where acatalyst support is employed, the support will generally constitute fromabout 10 to about 98, preferably from about 75 to about 95, weightpercent of the total catalyst composition. Supports having a surfacearea in the range of about 2 to about 50 m' lg, preferably in the rangeof about 5 to about 20 mQ /g, are desirable. Where the promoter is iron,nickel or cobalt, the atom ratio of promoter to vanadium will generallybe in the range of about 50:] to about 2:], and preferably will be inthe range of about 5:l to about 2:l For the iron, nickel or cobaltpromoted catalyst, the atom ratio of the total of vanadium and promoterto phosphorus will generally be in the range of about 03:1 to about land preferably will be in the range of about: 0.4:l to about 6:1. Theatom ratio of molybdenum to vanadium will generally be in the range ofabout 12:1 to about O.l:l, preferably in the range of about l0:l toabout 0.521. [f the catalyst composition does not contain a supportmaterial, the atom ratio of the total of vanadium and molybdenum tophosphorus will generally be in the range of about 40:] to about 2:],preferably in the range of about 30:] to about 4:]. Where a solidcatalyst support is utilized, the atom ratio of the total of molybdenumand vanadium to phosphorus will generally be in the range of about 7:1to about 0.05:], preferably in the range of about 5:l to about O.l:l.

The catalysts of the present invention can be prepared by many suitabletechniques, for example coprecipitation, impregnation, ion exchange,aqueous or nonaqueous solution or suspension mixing or dry mixing. Ingeneral, any method can be employed which will provide a compositioncontaining the desired elements in the defined proportions, and whichhas a catalytic surface area in the range of about 0.05 to about 20 m/g, preferably about 0.] to about 5 m /g. Thus, the catalyst componentsand/or compounds thereof can be combined in any suitable manner. Anycompound of vanadium, phosphorus or the promoter can be employed in thepreparation of the catalyst so long as none of the compounds aredetrimental to the final oxidative dehydrogenation catalyst andessentially all of the elements in the compounds employed, other thanthe vanadium. phosphorus, promoter metal and oxygen, are removed fromthe final catalyst by washing or by volatilization. However, small ortrace amounts or some other elements which can be involved in thepreparation of the catalyst can be tolerated in the final catalyticcomposition. For example, if alkali metal or alkaline earth metalhydroxides are employed in the preparation of the catalyst, very smallresidual amounts of such alkali metal and alkaline earth metals are notdetrimental. Similarly, if nickel sulfate, cobalt sulfate and ironsulfate are employed in the preparation of the catalyst, small residualamounts of sulfur can be tolerated.

Generally, however, the preferred vanadium, iron, cobalt, nickel andmolybdenum compounds are the oxides or phosphates of these elements orcompounds which are converted to the oxide or phosphate on calcination.The preferred phosphorus compounds include the phosphorus oxides, thephosphatesIof the various metals employed in the catalyst as well as theammonium phosphates; and the various forms of phosphoric acid, andadmixtures thereof. Thus, suitable. compounds include the oxides,phosphates, nitrates, ha-

lides, sulfates, joxalates, acetates, carbonates, propionates,tart-rates, hydroxides, molybdates, vanadates, and the like, andmixtures thereof. Examples of these compounds include cobalt nitrate,cobalt acetate, cobalt hydroxide, cobalt oxide, cobalt propionate, ironoxide, iron nitrate, iron acetate, molybdenum oxide, ammonium molybdate,molybdenum phosphate, phosphoric acid, nickel oxide, nickel chloride,nickel nitrate, nickel carbonate, phosphorus pentoxide, diammoniumhydrogen phosphate, cobalt phosphate, iron phosphate, nickel phosphate,vanadium oxide, vanadium phosphate, ammonium vanadate, and the like, andadmixtures thereof. The term phosphate includes not only themonophosphate ion, POI, but also polyphosphate ions (PnO;,,, and [PnO(OH):]" in which n is an integer in the range of 2 through 100.

One technique for forming an unsupported catalyst of the presentinvention comprises mixing one or more phosphorus compounds, one or morevanadium compounds, and one or more promoter metal compounds.

The compounds can be admixed in the form of dry compounds and thencalcined. They can be admixed in the presence of a diluent to form apaste and/or one of the components can be employed in liquid form, suchas phosphoric acid, to form the paste. If desired the paste can be driedbefore calcining. A particle forming step such as pelletizing orscreening can precede the drying step or the calcining step.

A technique for forming a supported catalyst of the present inventioncomprises sequentially impregnating the support with solutions ordispersions of each com ponent compound, drying and calcining theimpregnated support.

The calcining step will be accomplished under conditions which ensurethe conversion of any nonoxide or nonphosphate compounds to the oxide orphosphate form and the volatilizing of any undesired elements. ingeneral, the calcining step comprises heating the catalyst compositionto a temperature in the range of about 800F to about 1500F for a time inthe range of about 1 to about 40 hours. Presently preferred calciningconditions comprise a temperature in the range of about 850F to about1400F for a time in the range of about 2 to about 24 hours in thepresence of a molecular oxygen-containing gas, for example, air.

Suitable feeds for conversion to furan compounds include the acyclicalkadienes having from 4 to 10 carbon atoms. Examples includebutadiene-1,3, pentadiene-l,3, isoprene, hexadiene-l,3, decadiene-l,3,and the like, and mixtures thereof. The acyclic alkadienes having from 4to 5 carbon atoms are presently preferred. in one embodiment of thepresent invention, acyclic alkenes can be contacted with the definedcatalyst to convert at least a portion thereof to acyclic alkadieneswhich can then be converted to the desired furan compounds. Examples ofsuitable acyclic alkenes having from 4 to carbon atoms include butene-l,butene-2, n-pentene-l isopentene, hexene-l, heptene- 2, octene-ldecene-l Z-methylbutene-l, hexene-3, 2- ethylbutene-l,2-methylpentene-3, 3-ethylhexene-2, and mixtures thereof.

The furan compounds produced by the process of the present inventionhave the formula wherein each R is individually selected from the groupconsisting of hydrogen and alkyl radicals having from 1 to 6 carbonatoms, the total carbon atoms in the R radicals being in the range of 0to 6. Representative products include furan, 2-methylfuran,3-methylfuran, 2,5-diethylfuran, 2-n-hexylfuran, 2-isopropyl-3-methylfuran, 3,4-n-dipropylfuran, 3-methyl-4-nbutylfuran and the like.

In accordance with the present invention a hydrocarbon feed comprisingone or more acyclic alkenes and- /or one or more acyclic alkadienes iscontacted, under suitable reaction conditions for conversion to furancompounds, with a molecular oxygen-containing gas in the presence of thehereinabove-defined catalyst. The molecular oxygen-containing gas can behigh purity oxygen, oxygen diluted with an inert diluent such asnitrogen, flue gas containing residual oxygen, air or any other sourceof molecular oxygen which is at least essentially free of contaminantswhich would be detrimental to the desired reaction. In a presentlypreferred embodiment, the oxidative dehydrogenation process is carriedout in the absence of any halogen. in general, the temperature will bein the range of about 500 F. to about l200 F., and preferably will be inthe range of about 700 F. to about 1 100 F. Any suitable pressure can beemployed, but, in general, the pressure will be in the range of about0.05 to about 250 psig, and preferably will be in the range of about 0.1to about 25 psig. The hydrocarbon feed rate will generally be in therange of about 10 to about 1000 standard cubic feet of alkenes and/oralkadienes per hour per cubic foot of catalyst bed (GHSV), andpreferably will be in the range of about to about 500 GHSV. The molratio of molecular oxygen to alkenes and alkadienes will generally be inthe range of about 0.1:] to about 3:1, and preferably will be in therange of about 0.5:1 to about 2:1. Steam can be employed in the reactionzone as a diluent and heat transfer agent. When steam is utilized, themol ratio of steam to alkenes and alkadienes will generally be in therange of about 0. 1:1 to about 50:], and preferably will be in the rangeof about 5:1 to about 30:].

The alkenes, if present, are largely converted to the correspondingalkadienes. The alkadienes, in turn, are converted in significantquantities to the corresponding furan compounds. However, the reactioneffluent can also contain unreacted feed material, alkenes includingethylene, propylene, and butenes, oxides of carbon, alkenylcycloolefins,crotonaldehyde, acetaldehyde, and other oxygenated products. The furancompounds can be recovered by suitable techniques, for example bycondensation from the reactor gas effluent followed by distillation.Unconverted alkenes and/or alkadienes can be recovered and recycled tothe reactor, as can other materials such as crotonaldehyde which areconvertible to furan compounds under the reaction conditions. Ifdesired, the conversion of alkenes to furan compoun'ds can be conductedin two reaction zones in series. The first reaction zone can be operatedunder conditions favorable for the conversion of the alkenes toalkadienes, while the second reaction zone can be operated underconditions favorable to the conversion of the alkadienes to furancompounds. The effluent from the first reaction zone can be subjected toconventional separation techniques to recover unconverted alkenes forrecycle to the first reaction zone and a concentrated alkadiene streamfor feed to the second reaction zone. If desired, the total effluentfrom the first reaction zone can be passed directly to the secondreaction zone without separation. The effluent of the second reactionzone can be processed for recovery and recycle of unreacted alkadienesto the second reaction zone and for recovery of a furan compoundproduct. The catalyst of the present invention can be employed in bothreaction zones, or another suitable dehydrogenation catalyst can beemployed in the first reaction zone while the present catalyst isutilized in the second reaction zone.

The following example is presented in further illustration of theinvention and should not be construed in undue limitation thereof.

EXAMPLE in each of a series of runs employing various catalysts,butadiene was contacted with molecular oxygen and steam in the presenceof the respective catalyst. The reaction conditions and results areshown in the following table. Two cubic centimeters of the respectivecatalyst was employed in each run! TABLE Promoter/- Atom Ratio M01 "/172 Vanadium Total Metal GHSV "/1 mol 71 72 Yield Selectivity Atom toButa- Conversion yield Selectivity Oxygenated Oxygenated emp.

Run Promoter Ratio Phosphorus F. diene Steam Butadiene Furan to FuranProducts Products 1 3/1 900 100 50 2000 28.7 7.2 25.0 10.1 35.2 2 3/11100100 50 2000 31.5 6.2 19.8 8.7 27.8 3 3]] 1100400 200 8000 8.9 2.629.6 3.4 38.0 4 3/1 900 400 200 8000 5.2 1.9 37.0 2.5 49.0 5 Co 4/10.5/1 1000400 400 8000 14.5 10.5 72.4 10.9 75.5 6 Ni 4/1 0.5/1 1000400400 8000 20.6 12.2 59.2 12.9 62.9 7 Fe 4.5/1 0.5/1 1000400 400 8000 10.16.8 67.3 10.6 71.4 8 Fe 45/1 5.7/1 700400 400 8000 24.1 6.1 25.3 7.029.2 9 Mo 8/1 13/1 1000400 400 8000 24.2 17.2 71.0 18.1 74.9 10 Mo 8/127/1 1000400 400 8000 25.5 16.7 65.5 18.1 70.9 11 Mo 8!] 7/1 1000400 4008000 13.5 9.9 73.3 10.3 75.6 12 Mo 2/1 16/1 900400 400 8000 26.0 12.849.2 13.3 51.2 13 Mo 8!] 4.5/1 1000400 400 8000 5.1 1.7 34.1 1.7 34.1 14Mo 8/1 4.5/1 1000400 400 8000 7.1 2.3 32.4 2.6 36.6 15 Mo 4/1 1.2/1900400 400 8000 16.4 7.9 48.1 8.1 49.2 16 Mo 4/1 1.2/l 1000400 400 80004.3 1.3 30.6 1.3 30.6 17 Mo 8/1 2.2/1 900400 400 8000 2.9 11.2 42.6 1.242.6 18 Mo 8/1 1.5/1 900400 400 8000 17.4 7.4 42.5 7.7 44.5 19 Mo 1/12/1 900400 400 8000 22.6 9.5 42.0 10.2 45.2 20 Mo 1/1 0.67/1 900400 4008000 24.0 9.6 40.0 10.2 42.4

The catalysts were generally prepared in small lots of about 20 grams orless using the amounts of each component required to give the atomratios shown in the Table. The catalysts of runs l-l4 were employedwithout supports.

The catalyst of runs 1-4 was made by mixing together phosphoruspentoxide and vanadium pentoxide and calcining the product for 16 hoursat 1000 F.

The catalysts of runs 5-8 were made by mixing to-.

the paste to dryness and calcining at 1000 F. The calcining times were16 hours for the catalysts of runs 9-1 1, 6 hours for the catalyst ofrun 12, and 8 hours for the catalyst of run 13.

The catalyst of run 14 was made by mixing together molybdenum trioxide.phosphoric acid, water and vanadium trioxide to form a paste,evaporating the paste to dryness and calcining the product at 1000 F.for 16 hours.

Supported catalysts were used in runs 15-20. The support in eachinstance was silica and the final composition contained about 8 weightpercent catalyst and 92 weight percent silica. Each composition was madeby impregnating the support with a solution formed by dissolving therequisite quantities of ammonium molybdate and ammonium vanadate indilute phosphoric acid and evaporating the composite to dryness. Thecomposite was calcined at 1000 F. for 4 hours.

The gaseous effluents. on a dry basis, were analyzed by means ofgas-liquid chromatography. Products found included unreacted butadiene,furan, acetaladehyde, carbon oxides, ethylene, propylene and butenes.The reported selectivities to furan and furan plus acetaldehyde aremodified selectivities based on the above gaseous product analyses. Theyields of furan and acetaldehyde are in terms of mols per mols ofbutadiene feedstock. The oxygenated products reported in the Table arefuran and acetaldehyde.

The catalysts were normally tested at reactor temperatures of 700, 800,900 and 1000 F. in sequence. Data are reported only for those runs inwhich significant amounts of furan were produced.

The results show in general that promoting a vanadium/phosphorus/oxygencatalyst with a metal selected from the group consisting of cobalt,iron, nickel,-

and molybdenum in accordance with the invention can significantlyimprove the conversion of butadiene to furan and acetaldehyde, and tofuran in particular. The selectivity to the oxygenated products is also,in general, improved by using the catalysts of the instant invention.

Reasonable variations and modifications are possible within the scope ofthe foregoing disclosure and the appended claims to the invention.

That which is claimed is:

1. A process which comprises reacting oxygen and at least oneunsaturated acyclic feed hydrocarbon selected from the group consistingof alkenes and alkadienes having from 4 to 10 carbon atoms, in contactwith a catalyst comprising phosphorus, vanadium. oxygen and cobalt undersuitable reaction conditions for conversion of said at least oneunsaturated acyclic feed hydrocarbon to at least one furan compoundhaving the formula wherein each R is individually selected from thegroup consisting of hydrogen and alkyl radicals having from 1 to 6carbon atoms, the total carbon atoms in the R radicals being in therange of O to 6; and recovering at least a portion of the furancompounds thus produced.

2. A process in accordance with claim 1 wherein the cobalt/vanadium atomratio is in the range of about 50:1 to about 2:1 and the atom ratio ofthe total of cobalt and vanadium to phosphorus is in the range of about0.3:1 to about 10:1.

3. A process in accordance with claim 1 wherein the cobalt/vanadium atomratio is in the range of about 5:1 to about 2:1 and the atom ratio ofthe total of cobalt and vanadium to phosphorus is in the range of about0.4:1 to about 6:1.

4. A process accordance with claim 3 wherein said reaction conditionscomprise a temperature in the range of about 500F to about 1200F, anunsaturated acyclic hydrocarbon feed rate in the range of about 10 toabout 1000 GHSV, and a mol ratio of oxygen to unsaturated acyclic feedhydrocarbon in the range of about 0.1:1 to about- 33:1.

5. A process which comprises rseacting oxygen and at least oneunsaturated acyclic feed hydrocarbon selected from the groupconsistingIof alkenes and alkadienes having from 4 to 10 carbon atoms,in contact with a catalyst comprising phosphoriiis, vanadium, oxygen andnickel under suitable reaction conditions for conversion of said atleast one unsaturated acyclic feed hydrocarbon to at least one furancompound having the formula wherein each R is individually selected fromthe group consisting of hydrogen and alkyl radicals having from 1 to 6carbon atoms, the total carbon atoms in the R radicals being in therange of to 6; and recovering at least a portion of the furan compoundsthus produced.

6. A process in accordance with claim 5 wherein the nickel/vanadium atomratio is in the range of about 50:1 to about 2:1 and the atom ratio ofthe total of nickel and vanadium to phosphorus is in the range of about0.3:] to about :1.

7. A process in accordance with claim 5 wherein the nickel/vanadium atomratio is in the range of about 5:1 to about 2:1 and the atom ratio ofthe total of nickel and vanadium to phosphorus is in the range of about0.4:1 to about 6:1.

8. A process in accordance with claim 7 wherein said reaction conditionscomprise a temperature in the range of about 500F to about 1200F, anunsaturated acyclic hydrocarbon feed rate in the range of about 10 toabout 1000 GHSV, and a mol ratio of oxygen to unsaturated acyclic feedhydrocarbon in the range of about 0.1:1 to about 3:1.

9. A process which comprises reacting oxygen and at least oneunsaturated acyclic feed hydrocarbon selected from the group consistingof alkenes and alkadienes having from 4 to 10 carbon atoms, in contactwith a catalyst comprising phosphorus, vanadium, oxygen and iron undersuitable reaction conditions for conversion of said at least oneunsaturated acyclic feed hydrocarbon to at least one furan compoundhaving the formula wherein each R is individually selected from thegroup consisting of hydrogen and alkyl radicals having from 1 to 6carbon atoms, the total carbon atoms in the R radicals being in therange of 0 to 6; and recovering at least a portion of the furancompounds thus produced.

10. A process in accordance with claim 9 wherein the iron/vanadium atomratio is in the range of about 50:1 to about 2:1 and the atom ratio ofthe total of iron and vanadium to phosphorus is in the range of about0.3:] to about 10:1.

1 l. A process in accordance with claim 9 wherein the iron/vanadium atomratio is in the range of about 5:1 to about 2:1 and the atom ratio ofthe total of iron and vanadium to phosphorus is in the range of about0.4:] to about 6:1.

12. A process in accordance with claim 11 wherein said reactionconditions comprise a temperature in the range of about 500F to about1200F, an unsaturated acyclic hydrocarbon feed rate in the range ofabout 10 to about 1000 GHSV, and a mol ratio of oxygen to unsaturatedacyclic feed hydrocarbon in the range of about 0.1:1 to about 3:].

13 A process which comprises reacting oxygen and at least oneunsaturated acyclic feed hydrocarbon selected'from the group consistingof alkenes and alkadienes having from 4 to 10 carbon atoms, in contactwith an unsupported catalyst consisting essentially of phosphorus,vanadium, oxygen and molybdenum under suitable reaction conditions forconversion of said at least one unsaturated acyclic feed hydrocarbon toat least one furan compound having the formula wherein each R isindividually selected from the group consisting of hydrogen and alkylradicals having from 1 to 6 carbon atoms, the total carbon atoms in theR radicals being in the range of O to 6; the atom ratio ofmolybdenum/vanadium being in the range of about 12:1 to about 0.1:], andthe atom ratio of the total of molybdenum and vanadium to phosphorusbeing in the range of about 40:1 to about 2:1; and recovering at least aportion of the furan compounds thus produced.

14. A process in accordance with claim 13 wherein the atom ratio ofmolybdenum to vanadium is in the range of about 2:1 to about 8:1 and theatom ratio of the total of molybdenum and vanadium to phosphorus is atleast about 7:1.

15. A process in accordance with claim 14 wherein the atom ratio ofmolybdenum to vanadium is about 8: 1.

16. A process in accordance with claim 13 wherein said reactionconditions comprise a temperature in the range of about 500F to about1200F, an unsaturated acyclic hydrocarbon feed rate in the range ofabout 10 to about 1000 GHSV, and a mol ratio of oxygen to unsaturatedacyclic feed hydrocarbon in the range of about 0.121 to about 3:1. 1

1. A PROCESS WHICH COMPRISES REACTTTING OXYGEN AND AT LEAST ONEUNSATURATED ACYCLIC FEED HYDROCARBON SELECTED FROM THE GROUP CONSISTINGOF ALKENES AND ALKADIENES HAVING FROM 4 TO 10 CARBON ATOMS, IN CONTACTWITH A CATALYST COMPRISING PHOSPHORUS, VANADIUM, OXYGEN AND COBALT UNDERSUITABLE REACTION CONDITIONS FOR CONVERSION OF SAID AT LEAST ONEUNSATURATED ACYCLIC FEED HYDROCARBON TO AT LEAST ONE FURAN COMPOUNDHAVING THE FORMULA
 2. A process in accordance with claim 1 wherein thecobalt/vanadium atom ratio is in the range of about 50:1 to about 2:1and the atom ratio of the total of cobalt and vanadium to phosphorus isin the range of about 0.3:1 to about 10:1.
 3. A process in accordancewith claim 1 wherein the cobalt/vanadium atom ratio is in the range ofabout 5:1 to about 2:1 and the atom ratio of the total of cobalt andvanadium to phosphorus is in the range of about 0.4:1 to about 6:1.
 4. Aprocess in accordance with claim 3 wherein said reaction conditionscomprise a temperature in the range of about 500*F to about 1200*F, anunsaturated acyclic hydrocarbon feed rate in the range of about 10 toabout 1000 GHSV, and a mol ratio of oxygen to unsaturated acyclic feedhydrocarbon in the range of about 0.1:1 to about 3:1.
 5. A process whichcomprises reacting oxygen and at least one unsaturated acyclic feedhydrocarbon selected from the group consisting of alkenes and alkadieneshaving from 4 to 10 carbon atoms, in contact with a catalyst comprisingphosphorus, vanadium, oxygen and nickel under suitable reactionconditions for conversion of said at least one unsaturated acyclic feedhydrocarbon to at least one furan compound having the formula
 6. Aprocess in accordance with claim 5 wherein the nickel/vanadium atomratio is in the range of about 50:1 to about 2:1 and the atom ratio ofthe total of nickel and vanadium to phosphorus is in the range of about0.3:1 to about 10:1.
 7. A process in accordance with claim 5 wherein thenickel/vanadium atom ratio is in the range of about 5:1 to about 2:1 andthe atom ratio of the total of nickel and vanadium to phosphorus is inthe range of about 0.4:1 to about 6:1.
 8. A process in accordance withclaim 7 wherein said reaction conditions comprise a temperature in therange of about 500*F to about 1200*F, an unsaturated acyclic hydrocarbonfeed rate in the range of about 10 to about 1000 GHSV, and a mol ratioof oxygen to unsaturated acyclic feed hydrocarbon in the range of about0.1:1 to about 3:1.
 9. A process which comprises reacting oxygen and atleast one unsaturated acyclic feed hydrocarbon selected from the groupconsisting of alkenes and alkadienes having from 4 to 10 carbon atOms,in contact with a catalyst comprising phosphorus, vanadium, oxygen andiron under suitable reaction conditions for conversion of said at leastone unsaturated acyclic feed hydrocarbon to at least one furan compoundhaving the formula
 10. A process in accordance with claim 9 wherein theiron/vanadium atom ratio is in the range of about 50:1 to about 2:1 andthe atom ratio of the total of iron and vanadium to phosphorus is in therange of about 0.3:1 to about 10:1.
 11. A process in accordance withclaim 9 wherein the iron/vanadium atom ratio is in the range of about5:1 to about 2: 1 and the atom ratio of the total of iron and vanadiumto phosphorus is in the range of about 0.4:1 to about 6:1.
 12. A processin accordance with claim 11 wherein said reaction conditions comprise atemperature in the range of about 500*F to about 1200*F, an unsaturatedacyclic hydrocarbon feed rate in the range of about 10 to about 1000GHSV, and a mol ratio of oxygen to unsaturated acyclic feed hydrocarbonin the range of about 0.1:1 to about 3:1.
 13. A process which comprisesreacting oxygen and at least one unsaturated acyclic feed hydrocarbonselected from the group consisting of alkenes and alkadienes having from4 to 10 carbon atoms, in contact with an unsupported catalyst consistingessentially of phosphorus, vanadium, oxygen and molybdenum undersuitable reaction conditions for conversion of said at least oneunsaturated acyclic feed hydrocarbon to at least one furan compoundhaving the formula
 14. A process in accordance with claim 13 wherein theatom ratio of molybdenum to vanadium is in the range of about 2:1 toabout 8:1 and the atom ratio of the total of molybdenum and vanadium tophosphorus is at least about 7:1.
 15. A process in accordance with claim14 wherein the atom ratio of molybdenum to vanadium is about 8:1.
 16. Aprocess in accordance with claim 13 wherein said reaction conditionscomprise a temperature in the range of about 500*F to about 1200*F, anunsaturated acyclic hydrocarbon feed rate in the range of about 10 toabout 1000 GHSV, and a mol ratio of oxygen to unsaturated acyclic feedhydrocarbon in the range of about 0.1:1 to about 3:1.